Invasion and metastasis are predominantly reasons for the poor prognosis of cancers. Destructions of the neighbor and distant organs by cancer invasion and metastasis lead to loss of chance for surgical resection and recurrence after curative treatments. Sensitive biomarkers for detection of potential of invasion and metastasis would greatly improve the personalized clinical management for cancer patients. Therefore, predicting the invasion and metastasis potential of cancers is eagerly awaited.
It is well recognized that it is virtually impossible to identify metastasis potential of cancers based on histopathologic grounds alone. So it is expected to make molecular subtyping using the molecular biology methods. Great progress has been achieved on the expression change of protein and RNA in the past decades. Although there are many studies on cancer biology, the effectual method is still unavailable to accurately recognize the metastasis ability of cancer cells.
As the rapid development of molecular biology, people have got a comprehensive understanding on the mechanisms of carcinogenesis. In addition to the genetic inactivation or activation of tumor related genes (including p53, APC and Ras, etc.), epigenetic inactivation of tumor suppressor genes (including p15, p16 and hMLH1, etc.) by hypermethylation and reactivation of proto-oncogenes by hypomethylation of CpG islands are other kinds of frequent events in cancers. It is well known that detection of alterations of protein levels and mRNA levels of genes in a few abnormal cells in tissue samples is very difficult using regular gene expression assays, because their visibility would be greatly reduced by the co-existence of main cell populations in which the gene expression has not changed. In contrast, methylated and demethylated CpG islands can be analyzed with methylation- and demethylation-specific assays, respectively. This makes the detection of the methylation status of CpG islands so sensitive that methylation alterations that occurred in a few cells in a testing tissue can be clearly displayed. This makes DNA methylation an optimal biomarker for molecular stratification of cancers.
Receptor GFRa1 combines with Glial cell line-Derived Neurotrophic Factor (GDNF), forming the phosphotyrosine kinase [Cell 1996, 85(7):1113-1124] of the oncogene RET which is capable of activating the signaling pathways such as SRC, MAPK, AKT and Rho, etc. It is closely related to the proliferation, differentiation and migration of the cells [Nature Reviews Neuroscience 2002, 3(5):383-394]. It has been discovered that GFRa1 expression is elevated in the tissues of a number of cancers (such as pancreatic cancer, breast cancer, olfactory cell carcinoma and the glial cell tumor). Elevated expression of this gene promotes the occurrence, development and metastasis of these cancers [Cancer Research 2005, 65(24):11536-11541; Cancer Research 2007, 67(24): 11733-11741]. It has also been reported that the methylation-deactivation of GDNF, the ligand of GFRa1, is related to the occurrence of gastric cancer [Gastroenterology 2009; 136:2149-2158]. But there is no report on the method of using the methylation and demethylation of GFRa1 CpG islands to estimate the occurrence, metastasis and survival of tumors.